Actinic Radiation Curable Coating Compositions

ABSTRACT

A method of preparing a cured coating or molded article prepared from a composition comprising an actinic-radiation curing polymer, wherein the composition is cured with actinic radiation at a temperature of at most 150° C. to form the cured coating or molded article; wherein the cured coating or molded article has a thickness of at least about 0.5 mm and a hardness of about Shore A 90 to about Shore D 90

RELATED APPLICATION

This application is a divisional application of U.S. Ser. No. 11/139,508filed May 31, 2005, allowed, the disclosure of which is incorporated byreference in its entirety.

FIELD OF THE INVENTION

The present invention relates to transparent, high build, coatings andmolded articles using actinic-radiation-curable coating materials.

BACKGROUND OF THE INVENTION

The casting of a two-component, clear polyurethane resin upon asubstrate to produce a decorative emblem is well known in the art. Castpolyurethane, when cured, gives a lens effect to the surface applied asdescribed in U.S. Pat. No. 4,100,010 and RE 33,175. These castpolyurethane resins are commonly referred to as “doming” or “lensing”resins. Doming or lensing resins are typically clear, colorless, highgloss, room temperature or elevated temperature curing, thermosettingsystems developed to provide aesthetic enhancement and environmentalprotection to objects such as, but not limited to, paper, plastic, wood,metal, labels, decals, plaques, badges, name plates, lapel pins,automotive ornamentation, and automotive dashboards to form a durablethree-dimensional coating or dome.

In order for a liquid doming resin to achieve the required appearance onan object once it is cured, it preferably has a number ofcharacteristics intrinsic to both the liquid components and the curedresin. First, the formulation should be a clear, colorless, lowviscosity liquid. It should flow sufficiently to cover the entiresurface to which it is applied. It should produce a coating fromapproximately 20 mils (0.5 mm) to 100 mils (2.5 mm) high. It shouldfully cure within forty-eight hours at 25° C. & 50% R.H. The curing ofthe coating resin formulation should not cause shrinkage, wrinkles,surface defects, curling, or other deviations from a clear, transparent,smooth, high gloss surface. It should not contain volatile solvents(less than 1%). Once cured, the coating should maintain its initialhardness and flexibility after heat and environmental aging.

Doming resins typically have an application viscosity of about 100 to5000 cps, are generally clear and colorless, and cure to a smooth,defect free, flexible or rigid coating. In addition to protecting thesubstrate surface from the environment, the resins are usuallytransparent providing an aesthetically appealing lensing effect to thepattern, design, or scripting on or near the substrate surface overwhich the resins are placed.

Currently, conventional doming resins are practically applied astwo-component, 100% solids, polyurethane systems, which may be roomtemperature cured or cured with heat. Two-component epoxy systems aresometimes used in indoor applications. However, they cannot be usedoutdoors or in applications where they will be exposed to a highconcentration of UV light, as they will yellow. Polyurethane systems,based primarily on aliphatic diisocyanates, are used for most indoor andoutdoor applications.

There are major disadvantages with these two-component conventionalsystems.

They need specialized two-component metering-mixing and dispensingsystems to accurately dispense and mix the two reactive components. Thecuring of these resins must be made sufficiently slow so that the resindoes not cure in the mixing unit. However, the resins then cure slowlyonce dispensed onto the desired substrate. Smaller parts cure slowerthan larger parts. Tack-free times are usually greater than six hours atambient temperatures with full cure taking up to five days. Vacuumtables are often used to keep the substrate flat until the resinthickens sufficiently so that it will not flow off of the part. This cantake hours at ambient temperatures.

Special safety precautions are also necessary due to the inherenttoxicity of isocyanate and epoxy resin components in these formulations.Additionally, in isocyanate-functional systems, outgassing can occurwhen the isocyanate component undesirably reacts with a source of wateror carboxyl groups and not the hydroxyl groups present in the firstcomponent. This will cause carbon dioxide bubbles to generated & becomeentrapped in the cured product, essentially ruining the appearance andprotective properties of the coating.

Compounds based on the heavy metals; especially mercury and lead, arecommonly used as catalysts in these polyurethane based systems. Thesecompounds present both safety and environmental concerns. Phenylmercuric acetate is one example of such a catalyst.

Furthermore, polyurethane-based systems cannot be made softer than about70 Shore A. Thus, they cannot be used on pressure sensitive adhesivelabels for applications requiring a very soft, flexible dome, such as onhighly curved surfaces, unless very strong adhesives are used.

These two-component polyurethane and epoxy systems are also used inmolding applications to produce molded designs, nameplates, andlettering and in scripting and design applications. Here again thesesystems are limited by their long curing times and usually must be leftto cure at least twenty-four hours before they can be packaged.

Heat curing systems to accelerate the curing process are available.However they are expensive and require at least twenty minutes at 60° C.for the epoxies and polyurethanes to reach a tack free state. Afterthat, they again must sit for at least twenty-four hours before themolded parts and letters can be packaged.

One-component, thin coatings that cure by actinic radiation areextensively used for thin coatings. These coatings are usually appliedat less than 5 mils thick (0.13 mm). High build (>10 mils) UV curablecoatings are severely limited because of high shrinkage during thecuring process. Because of this high shrinkage these coatings have poorflexibility and poor adhesion to many substrates. This high shrinkagealso limits the use of these UV curing doming resins to very smallparts, usually less than 3 cm diameter. If placed on larger parts, suchas flexible labels or decals, the shrinking would cause the part to curlon curing. Furthermore, these systems yellow on exposure to UV light andcannot be used in outdoor applications. Furthermore, acrylic monomersare very expensive and these systems contain high acrylic monomercontents. There are also health concerns over the toxicity andsensitizing properties of the acrylate based functional monomers.

Co-pending application Ser. No. 11/124,077 describes one-componentsilylated, high build coatings that can also be used in doming resinapplications. These silylated systems have many advantages overtwo-component systems. They do not require two-component,meter-mix-dispensing systems, they do not produce carbon dioxide bubbleson exposure to moisture and they do not contain heave metals. Althoughthe application is useful for many applications, the tack-free times arein the area of thirty minutes to two hours.

Dual cure compositions have been used for structural adhesives such asdescribed in EP 646632A1, WO 0105846 and WO 98/53008. A photocurableresin composition for use in coatings comprising a component with dualfunctionality, acrylate and silane, is described in EP 0549228B1.

There is a need for a curing system that can be used in doming,scripting, and molding applications that cures quickly or instantly,does not shrink, has good UV light and weathering resistance, and can bepackaged as soon as it has been cured.

SUMMARY OF THE INVENTION

The present invention relates to transparent, high build, coatingsprepared from actinic radiation curable polymers, optionally withadditional alternative curable polymers. In one particular embodiment,the present invention is directed to a low- or non-toxic instant-curingdoming resin composition comprising at least an actinic-radiation curingpolymer.

The composition has low viscosity, and is easy to dispense, process, andcure. The composition has high build and, once cured, is flexible. Thecomposition contains a very low or no monomer content depending onacceptable exotherm levels/values. Shrinkage during cure is much lowerthan standard actinic-radiation curing formulations and is comparable totwo-component polyurethane formulations. Properties in the liquid andcured states are also comparable to two-component polyurethane coatingsystems. It has excellent adhesion to many substrates and can beformulated to have excellent outdoor weathering properties. It does nothave the inherent drawbacks of current actinic-radiation curing systems.

One embodiment of the present invention is directed to an articlecomprising a substrate and a cured coating; wherein the coating isprepared from a composition comprising an actinic-radiation curingpolymer, wherein the composition is cured with actinic radiation at atemperature of at most 150° C. to form the cured coating; wherein thecured coating has a thickness of at least about 0.5 mm and a hardness ofabout Shore A 90 to about Shore D 90.

Another embodiment of the present invention is directed to a moldedarticle prepared from a composition comprising an actinic-radiationcuring polymer, wherein the composition is cured with actinic radiationat a temperature of at most 150° C. to form the cured molded article;wherein the molded article has a thickness of at least about 0.5 mm anda hardness of about Shore A 90 to about Shore D 90.

The actinic-radiation curing polymer may be an acrylate polymer or amixture of acrylate polymers, such as selected from the group consistingof epoxy acrylates, urethane acrylates, polyester acrylates, polyetheracrylates, amine-modified polyether acrylates, acrylic acrylates, andmixtures thereof. Preferably the acrylate polymer is a urethaneacrylate.

The actinic-radiation curing polymer may also be a UV cationic curingpolymer such as those selected from the group consisting ofcycloaliphatic epoxy resins, caprolactone polyols, diglycidal ether ofbisphenol A, monoepoxides and vinyl ethers.

The composition has a viscosity of 50 to 20,000 cps, preferably fromabout 100 to about 10,000 cps, more preferably about 300 to about 5000cps.

In a further embodiment, the composition further comprises atwo-component epoxy or polyurethane polymer such as an aliphaticisocyanate polyurethane.

In another further embodiment the composition further comprises amoisture-curable silylated resin composition.

The composition typically further comprises at least one photoinitiatorand may contain at least one of the following flow agents, viscositymodifiers, foam control agents, plasticizing agents, moisturescavengers, adhesion promoters, temperature stabilizers, ultravioletradiation stabilizers, or colorizing additives.

The present invention is further directed to a method of preparing anarticle comprising a substrate and a cured coating; comprising preparinga composition comprising an actinic-radiation curing polymer, applyingthe composition to the substrate to form coating having a thickness ofat least about 0.5 mm and curing the composition with actinic radiationwhile maintaining a temperature of at most 150° C. to form the curedcoating; wherein the cured coating has a hardness of about Shore A 90 toabout Shore D 90. Preferably the coating is cooled during curing.

The present invention is further directed to a method of preparingmolded articles comprising preparing a composition comprising anactinic-radiation curing polymer, pouring the composition into a moldhaving a thickness of at least about 0.5 mm and curing the compositionwith actinic radiation while maintaining a temperature of at most 150°C. to form the molded article; wherein the cured molded article has ahardness of about Shore A 90 to about Shore D 90. Preferably the coatingis cured.

The present invention is further directed to a method of decreasing tackfree cure-time of a two-part polyurethane or epoxy compositioncomprising adding to the composition a sufficient amount of anactinic-radiation curing polymer to reduce the tack-free time, and thenapplying actinic radiation to the composition while maintaining atemperature of at most 150° C. Preferably application of the actinicradiation forms a skin on the outside of the coating.

The present invention is further directed to a method of decreasing tackfree cure-time of a moisture curable silylated composition comprisingadding to the composition a sufficient amount of an actinic-radiationcuring acrylate polymer or acrylate monomer to reduce the tack-freetime, and then applying actinic radiation to the composition.Preferably, application of the actinic radiation forms a skin on theoutside of the coating.

These dual-curing systems are also capable of shadow cure.

DETAILED DESCRIPTION OF THE INVENTION

Actinic-radiation curing has been used to provide resin systems thatcure at high speed at room temperature upon exposure to the appropriateenergy, thus improving productivity. Actinic radiation iselectromagnetic radiation such as near infrared, visible light, UVlight, or X-rays, in particular UV light, or corpuscular radiation suchas an electron beam. Ultraviolet radiation and electron beam curing alsoreduces volatile organic compound emissions.

Success has been achieved and technical information is readily availableon thin (<5 mils) radiation curable coatings. However, high buildcoatings differ from low build coatings and little information isavailable for high-build coatings and doming resins (>20 mils thick).

In high build coatings, radiation must penetrate through much thickersections than low build coatings. Because of the greater mass in highbuild coatings, a much higher exotherm is realized during cure and heatdissipation is much slower. Shrinkage from high exotherm temperatures isalso more pronounced in high build coatings. The present invention isbased on discovery of a polymer system and process conditions thatovercome these difficulties of prior art high build coatings.

The present invention is directed to doming (high build) compositionscontaining at least one actinic-radiation curable polymer, andoptionally, additional alternative cure polymers. A single curing systemis obtained using the actinic-radiation curable polymer without theaddition of alternative curing polymers. A dual-curing system isobtained when the polymer is combined with a second polymer such as atwo-component polyurethane or epoxy or a moisture-curing silylatedpolymer.

The actinic-radiation curing composition has a viscosity from about 50to about 20,000 cps, preferably from about 100 to about 10,000 cps, morepreferably about 300 to about 5000 cps. This range provides a balanceamong such factors as ease of pouring, ability to generate a dome ofapproximately 0.5 to 2 mm high, and the ability to flow to the edge ofthe part and stop. Much higher domes are possible if they are molded.

During application of the actinic radiation, the temperature of thecoating should be less than 150° C., preferably less than 100° C., andmore preferably less than 70° C. This minimizes linear shrinkage,curling of flexible articles, and improves adhesion to flexible andrigid articles. Preferably, linear shrinkage is kept below 2% andpreferably below 1%. The temperature may be maintained by any suitablecooling means.

The actinic-radiation curable may be an acrylate polymer or mixture ofacrylate polymers. Acrylate polymer may be selected from epoxyacrylates, urethane acrylates, polyester acrylates, polyether acrylates,amine modified polyether acrylates or acrylic acrylates. One skilled inthe art is familiar with the manufacture of these polymers.

A preferred acrylate polymer is a urethane acrylate. Aliphatic urethaneacrylates possess the excellent weathering properties required foroutdoor applications. The urethane acrylate provides flexibility,toughness, hardness, and weathering properties to the actinic-radiationcurable coating.

Acrylate monomers used to prepare the acrylate polymers can bemonofunctional, difunctional or trifunctional. Because addition ofacrylate monomers to the UV-curing polymer will increase the shrinkageof the composition, acrylic monomers are generally kept to a minimum.For instance, the amount of monomers depends on acceptable exotherm.Shrinkage is typically more pronounced in thicker films and coatingsthan in thinner films and coatings. It was discovered that replacing theacrylic monomers with approximately equal quantities of vinyl ethersreduced the exotherm, reduced the shrinkage, and caused a greaterviscosity reduction.

In general, polyurethane acrylates, polyester acrylates, epoxyacrylates, and acrylic acrylates with higher functionality will shrinkmore than those with lower functionality. Therefore, monofunctional anddifunctional acrylates are preferred over acrylate polymers with higherfunctionality, although polymers with higher functionality can also beused.

Heat is generated when the actinic-radiation curing resin is exposed tohigh intensity light. Higher temperatures are reached and the heat isretained longer in thick coatings than in thin coatings. For example, a0.08″ thick UV-curing polymer reached a temperature of 240° C. onexposure to high intensity UV radiation for one second. The same resinat 0.001″ thick only reached a temperature of 50° C. This high exothermcauses high shrinkage of the coating. Shrinkage is not desired asflexible articles will tend to curl and adhesion will be difficult inboth flexible and rigid articles.

Generally, polymers with higher crosslinking density tend to shrink moreon curing than polymers with lower crosslinking density. In addition, apolymer that generates more heat on curing and has a higher exothermtends to shrink more than a similar polymer with a lower exotherm.Higher functional polymers of the same polymeric backbone will tend tohave a higher exotherm. Controlling the exotherm will help reduce theshrinkage.

Furthermore, since exposure to UV light is only for fractions of asecond, highly focused lamps with maximum intensity are required. Mostof these lamps also emit IR radiation which also contributes to heatingthe coating during the UV-curing process.

Besides formulating the UV-curable coating to have a low exotherm, it isalso possible to obtain the desired results of lower shrinkage bycooling the resin or the substrate to reduce the maximum temperaturethat the resin reaches during cure. This can be obtained by cooling thesubstrate, the resin, or both. This cooling is effective when appliedbefore, during, and immediately after exposure to the UV light, and maybe achieved by any suitable method or apparatus.

Another method of decreasing the shrinkage in thick coatings is to use alower light intensity over a longer period of time. However, this mayincrease the time it will take for the part to cure, slowing production,and increasing costs.

Generally, the composition when applied to a substrate at a thickness of2 mm at a temperature of 25° C. and a relative humidity of 50% typicallycures in one pass at a conveyor speed of 20 ft/minute.

The composition, when cured, will typically have a hardness of between10 Shore A and about 90 Shore D. The hardness can be controlled withdifferent polyols, isocyanates, acrylates and monomers, and differentcombinations thereof. Those skilled in the art are familiar how toformulate the UV-curing composition to obtain the desired hardness andother properties.

It was further discovered that combining the actinic-radiation curingpolymer and a second type of polymer provides doming resins and highbuild coatings having good tack-free times but low shrinkage. Suchpolymers are polyurethanes, epoxies, and silylated polymers. Thesecombinations provide single compositions having a dual-curecharacteristic.

The actinic radiation curable polymer can be present in quantities ashigh as 95 wt % of the formulation and as low as 5 wt % in thesesystems. Typically the range will fall between about 10 wt % to about 50wt %.

Suitable actinic-radiation curing polymers include both acrylatepolymers and UV cationic curing polymers. In acrylate polymers,aliphatic urethane based acrylates were found to be very suitablebecause of their good weathering properties. However, polyesteracrylates, polyether acrylates, aliphatic epoxy acrylates and acrylicacrylates can also be used. In cationic cure polymers, cycloaliphaticepoxy resins are used.

In the dual-cure systems, the compatibility between the polymers,acrylates or other unsaturated moieties can be improved by reacting theacrylate or other suitable monomer, onto the same molecule as theisocyanate or polyol of the two-component polyurethane or onto the samemolecule as the silane.

In one dual-cure system, a composition is prepared from anactinic-radiation curing polymer and a two-component polyurethane or atwo-component epoxy. This dual-cure system utilizes both energyradiation and the reaction of the two-component resin to cure thecomposition.

Two-component polyurethane and epoxy coatings are very slow to cure.They become tack-free in 6 hours or more and fully cure in twenty-fourhours of longer. Therefore, they have very low exotherms. Measuredexotherms are less than 5° C. for coatings cured at ambienttemperatures.

On the other hand, UV-curing resins, for example, react very quickly andhave very high exotherms. Increasing the concentration of UV curableresins results in higher exotherms and higher shrinkage. With largerconcentrations of the polyurethane, the wet and cured propertiesresemble the properties of the two-component polyurethane. The relativequantities of the two polymers can be changed to achieve the desiredliquid and cured properties. The two-component polyurethane provides lowliquid viscosity, low exotherm, low shrinkage, shadow cure and adhesion.The UV-curing polymer provides instant curing and tack-free time.Formulations for two-component polyurethane doming resins and high buildcoatings are described in U.S. Pat. No. 4,100,010 & RE. 33,175, forexample.

It was discovered that the combination of actinic-radiation curablepolymer and two-component polyurethane and epoxy polymers instantlyforms a “skin” on the surface of the coating upon irradiation withactinic-radiation. The combination cures sufficiently through the bodyof the resin so that the coated article can be moved easily without thecoating flowing over the edge of the substrate. This skin also preventsdust from being cured onto the surface of the coating. Shrinkage is verylow and comparable to two-component polyurethane doming resinformulations.

In another dual-cure system, a composition is prepared from anactinic-radiation curing polymer and a one-component moisture-curingsilylated polymer. In this dual-cure system, both actinic-radiation andmoisture are used in combination to cure the composition.

Formulations for the silylated polymers are described in co-pendingapplication Ser. No. 11/124,077, incorporated herein by reference in itsentirety.

The silylated polymer provides low shrinkage properties as well asflexibility, elongation, shadow cure and adhesion to the finishedproduct. The UV curable composition provides the instant cure andhardness. The relative quantities of the UV-curing polymer and thesilylated polymer can be changed to provide the desired liquid and curedproperties.

It was further discovered that the combination of an actinic-radiationcurable composition and a one-component, moisture curing silylatedpolymer would provide instant skinning of these compositions onirradiation. This allows the domed article to be lightly handledimmediately after exposure to the actinic-radiation. It also preventsdust and dirt from curing on the domed article.

It was further discovered that building certain properties into theactinic-radiation curing polymer would enhance desirable properties inthe silylated composition that are not easily attainable by thesilylated polymer alone. Such properties include flexibility, toughness,and hardness. Moreover shrinkage is much lower than UV curingformulations. Shrinkage is comparable to the shrinkage obtainable withsilylated systems alone. Example 14 illustrates how the hardness of asilylated polymer can be greatly increased with the addition of 10% ofan actinic-radiation curable polymer

The compositions may further comprise one or more photoinitiators. Foracrylate polymers, preferred photoinitiators are capable of initiatingfree radical polymerization, crosslinking, or both, of the ethylenicallyunsaturated moiety on exposure to radiation of a suitable wavelength andintensity. Cationic photoinitiators are used in UV cure cationic systemswhere the main part of the formulation is a cycloaliphatic-diepoxide.The photoinitiator can be used alone or in combination with a suitabledonor compound or a suitable coinitiator. The photoinitiator and theamount used are selected to achieve a uniform reaction conversion, as afunction of the thickness of the coating being cured. The photoinitiatorwill also determine the degree of total conversion so as to achieve thedesired initial handling strength.

The photoinitiator is preferably present in an amount sufficient toprovide the desired rate of photopolymerization. The amount will depend,in part, on the light source, the thickness of the layer to be exposedto the radiant energy and the extinction coefficient of thephotoinitiator at the wavelength. Typically, the photoinitiatorcomponent will be present in an amount of from about 0.01% by weight toabout 10% by weight, more preferably from about 0.01% by weight to about5% by weight. Preferred photoinitiators, for free radicalpolymerization, include acylphosphine oxides, which are preferablypresent in an amount from about 0.03% percent by weight to about 0.4% byweight.

Useful photoinitiators for free radical polymerization include, e.g.,“alpha cleavage type” photoinitiators, including, e.g., benzyl dimethylketal, benzoin ethers, hydroxyl alkyl phenyl ketones, benzoylcyclohexanol, dialkoxy acetophenones, 1-hydroxycyclohexyl phenyl ketone,trimethylbenzoyl phosphine oxides, methyl thio phenyl morpholino ketonesand morpholino phenyl amino ketones; hydrogen abstractingphotoinitiators, which include a photoinitiator and a coinitiator, basedon benzophenones, thioxanthones, benzyls, camphorquinones, andketocoumarins; and combinations thereof. Preferred photoinitiatorsinclude acetylphosphine oxides, including, e.g.,bis(2,4,6-trimethylbenzoyl)-phenylphosphine oxide,bis(2,6-dimethoxybenzoyl)-(2,4,4-trimethylpentyl)phosphine oxide, and2,4,4-trimethylbenzoyl diphenylphosphine oxide.

Useful commercially available free radical photoinitiators are availableas follows: IRGACURE 369, alpha-amino ketone; IRGACURE 819,bis(2,4,6-trimethylbenzoyl)-phenylphosphine oxide; IRGACURE 403,bis-(2,6-dimethoxybenzoyl)-(2,4,4-trimethylpentyl)phosphine oxide;IRGACURE 651, benzyldimethyl-ketal; IRGACURE 184,1-hydroxy-cyclohexylphenyl-ketone; DAROCUR 1173,2-hydroxy-2-methyl-1-phenyl-1-propanone; DAROCUR 4265, 50:50 blend of2-hydroxy-2-methyl-1-phenylpropan-1-one and2,4,6-trimethylbenzoyldiphenylphosphine oxide, and IRGACURE 1700, 25:75blend of bis(2,6-dimethoxybenzoyl)-2,4,4-trimethyl phenylphosphine oxideand 2-hydroxy-2-methyl-1-phenyl-propan-1-one. All these products areavailable from Ciba Geigy.

Common materials used in cationic UV curing systems are cycloaliphaticepoxy resins, caprolactone polyols, diglycidal ether of bisphenol A,monoepoxides and vinyl ethers. Common photoinitiators are mixed triarylsulfonium hexafluoroantimonate salts, mixed triaryl sulfoniumhexafluorophosphate salts and diaryl iodonium hexafluoroantimonatesalts. These materials are available from Dow Chemicals.

The composition may also include an effective amount of colorizingadditives to provide color effect to the cured formulation. Suitablecolorizing additives include, but are not limited to, inorganic pigmentssuch as those based on titanium dioxide, iron oxides, lead oxide,calcium carbonate, cobalt alumina hydrate, barium sulfate, zinc oxide,strontium, chrome, copper, or cobalt; or organic colorants such as thephthalocyanines, azos, perylenes, quinacridones, indanthrones, andpyrroles.

Other additives such as flow agents, viscosity modifiers, foam controlagents, plasticizing agents, moisture scavengers, adhesion promoters,temperature stabilizers, and/or ultraviolet radiation stabilizers may beadded. Flow agents typically include polyether modified organosilicones,such as Silwet® L-7602 or CoatOSil® 3500 surfactant (GE-OSi); DC-57Additive (Dow Corning); or Tego® Wet 260 additive (Degussa) Viscosityincreasing agents may include surface treated silica, while viscosityreducing agents may include plasticizers such as dioctyl phthalate,diisononyl phthalate, and diisodecyl phthalate. Moisture scavengers suchas molecular sieves, oxazolidines and/or vinyl trimethoxysilane areoften employed. Adhesion promoters may include organosilanes such asaminopropyltrimethoxysilane, aminopropyltriethoxysilane,aminoethyl-aminopropyltrimethoxysilane, N-phenylaminopropyltrimethoxysilane, glycidoxypropyltrimethoxysilane,(epoxycyclohexyl)ethyltrimethoxysilane; phosphate, titanate or chromiumesters, and zinc compounds. Examples of temperature stabilizers includethe Irganox® brands from Ciba specialty chemicals. For example, Irganox1010 Antioxidant. Light stabilizers of the hydroxyphenyl-s-triazinefamily were found to be most suitable for use in the high build, clearand pigmented doming resins; for example Tinuvin 400 from Ciba SpecialtyChemicals. However, other classes of UV absorbers can also be used,including the hydroxyphenyl-benzotriazoles, hydroxyl-benzophenones andoxalic anilides.

The composition may be applied to any suitable substrate where a highbuild, clear or pigmented, bubble free, one-component coating isdesired; such as decals, logos, badges, sealing, potting andencapsulating electronic and other components, photo-patterningapplications and other articles. The substrates can be either flexibleor rigid. Scripting and letter writing is also possible. Substratescontaining the domed resin may be used for decorative items, promotionalitems, decals, labels, nameplates, signs, high-build printed anddecorative lettering and designs, automotive decorations such as racingstripes and body designs and the like. Because these coatings haveexcellent weathering properties, items coated with them are protectedand may be used in exterior applications. These coatings can be used asa protective and decorative coating. They can also be used to producedecorative lettering, scripting, specialized inks such as inkjet inksand other decorations directly on a substrate or they can be applied toa substrate with a pressure sensitive or other types of adhesives. Theycan also be used to produce molded items. In this application they willbe poured into an open or closed mold and cured. These coatings can alsobe used for protection against mechanical shock, vibration, andtampering in applications such as potting compounds and conformationalcoatings. They can also be specially formulated to provide electricalinsulation or electrical conductivity. Other potential areas ofapplication include plastic eyeglass lens, automotive and recreationalvehicle headlight and tail light lens, cosmetic packaging and many otherparts.

Equipment Used

The UV-curing unit was model number LC-6 from Fusion UV Systems fittedwith a D-bulb and placed over a conveyor belt running at a speed ofapproximately 20′/minute. The UV dose delivered at that speed isapproximately 1000 mj/cm2 as measured by means of the “CONTROL-CURE®Compact Radiometer from UV Process Supply, Inc.

Shrinkage

Shrinkage of the coating was controlled in two ways.

First, linear shrinkage was kept below 2% and preferably below 1%.Linear shrinkage was determined by pouring the radiation curable polymerwith photoinitiator into a mold 12” long by 0.5″ wide by 0.125″ deep.The mold was passed under a high intensity UV lamp at a conveyor speedof 20″/minute. The length of the cured resin was measured and linearshrinkage determined. See Table 1 at end of examples.

The percentage of linear shrinkage can be obtained with followingequation.

${{Shrinkage}\mspace{14mu} (\%)} = {\frac{L_{u} - L_{c}}{L_{u}} \times 100}$

where, L_(u)—length of uncured sample,

-   -   L_(c)—length of cured sample.

Second, controlling the highest temperature the formulated coatingreaches while curing on the part also minimizes curling of flexiblearticles and improves adhesion to flexible and rigid articles. Thesurface temperature of the coating was measured with an infraredthermometer. This temperature should be less than 150° C., preferablyless than 100° C. and most preferably less than 70° C.

Some of the methods used to control the exotherm generated by thecoating are as follows:

-   -   Use oligomers that are less reactive, generally monofunctional        and difunctional oligomers are preferred over oligomers of        higher functionalities.    -   Use low monomer concentration. The reaction of monomers        increases the exotherm temperatures.    -   Use less reactive monomers. Monofunctional monomers are less        reactive than difunctional. Difunctional monomers are less        reactive than trifunctional.    -   Use acrylates with electron donor groups next to the unsaturated        group.    -   Acrylic unsaturation is preferred as it cures faster. However,        allylic or vinylic unsaturation may also be used as they will        contribute to a lower exotherm.    -   Plasticizers can also be used to decrease the exotherm        temperatures by reducing the concentration of reactive        materials.

Acrylate Monomers

It was also found that reactive acrylate monomers with the appropriatephotoinitiators can be used alone without acrylated oligomers to skinthe one-component silylated and the two-component polyurethane and epoxydoming resins. See Example 13

Monofunctional, difunctional,trifunctional, tetrafunctional and monomersof higher functionality can be used. However, generally better resultswere obtained with di and trifunctional, tetrafunctional and higherfunctionality monomers.

Cationic UV Curing Resins

Cationically cured photopolymers are similar to the free radically curedphotopolymers. They both show shrinkage and cause flexible decals tocurl if they exotherm above 70° C. during cure. The higher the exothermthe more they will shrink, the more the flexible decal will curl.

Cationic UV curing resins are also primarily applied as thin films (<6microns). They are known to have good adhesion and low shrinkage.Samples were prepared and results were compared to acrylated polymers.See Example 9.

Common materials used in cationic UV curing systems are cycloaliphaticepoxy resins, caprolactone polyols, diglycidal ether of bisphenol A,monoepoxides and vinyl ethers. Common photoinitiators are mixed triarylsulfonium hexafluoroantimonate salts, mixed triaryl sulfoniumhexafluorophosphate salts and diaryl iodonium hexafluoroantimonatesalts.

Examples Example 1

100% Urethane Acrylate

A urethane acrylate was prepared with IPDI, 4-hydroxybutyl acrylate, anda 4000 MW polyether diol in an equivalent ratio of 3/2/1. The reactionproduct was a clear, colorless liquid. At 25° C. the viscosity was11,000 cps.

The polymer was mixed with 1.8% Irgacure 184 photoinitiator and curedunder a high intensity UV lamp at a conveyor speed of 20′/minute. LinearShrinkage was 0.93% and Hardness was 84 D0.

Example 2

A doming resin formulation with good outdoor weathering properties wasprepared as follows:

Polymer from Example 1 100.0 Irgacure 184 1.8 Irgacure 819 0.1 Tinuvin1130 0.5 Tinuvin 292 0.5 Irganox 1010 0.5 Polyethelene Glycol Diacrylate10.0

This was a clear, transparent liquid with a viscosity of 7,000 cps.

The coating was poured onto a round, flexible decal of 2″ diameter. Thecoating was applied at a thickness of 0.08″. The decal was passed undera high intensity UV lamp at a conveyor speed of 20′/minute. The surfacetemperature of the coating was 90° C.

Adhesion was good. The cured coating had a 60° gloss of 84 and wastransparent. Some curling of the flexible decal was observed.

Example 3

100% Urethane Acrylate

A urethane acrylate was prepared with IPDI, hydroxypropyl acrylate and a1000 MW polyether diol in an equivalent ratio of 3/2/1. The reactionproduct was a clear, colorless liquid. At 25° C. the viscosity was 8,000cps.

The polymer was mixed with 1.8% Irgacure 184 photoinitiator and curedunder a high intensity UV lamp at a conveyor speed of 20′/minute. LinearShrinkage was 1.55% and Hardness was 40 D0.

Example 4

A doming resin formulation with good outdoor weathering properties wasprepared as follows:

Polymer in Example 2 100.0 Irgacure 184 1.8 Irgacure 819 0.1 Tinuvin1130 0.5 Tinuvin 292 0.5 Irganox 1010 0.5 Tetrahydrofurfuryl Acrylate10.0

This was a clear, transparent liquid with a viscosity of 4,000 cps.

The coating was poured onto a round, flexible decal of 2″ diameter. Thecoating was applied at a thickness of 0.08″. The decal was passed undera high intensity UV lamp at a conveyor speed of 20′/minute. The surfacetemperature of the coating was 115° C. Adhesion was poor. The curedcoating had a 60° gloss of 85 and was transparent. There was substantialcurling of the decal.

Example 5

100% Urethane Acrylate

A urethane acrylate was prepared with IPDI, hydroxyethyl acrylate and a1000 MW polyether diol in an equivalent ratio of 6/5/1. The reactionproduct was a clear, colorless liquid. At 25° C. the viscosity was166,000 cps.

The polymer was mixed with 1.8% Irgacure 184 photoinitiator and curedunder a high intensity UV lamp at a conveyor speed of 20′/minute. LinearShrinkage was 2.14% and Hardness was 84 D0.

Example 6

A doming resin formulation with good outdoor weathering properties wasprepared as follows:

Polymer in Example 5 100.0 Irgacure 184 1.8 Irgacure 819 0.1 Tinuvin1130 0.5 Tinuvin 292 0.5 Irganox 1010 0.5 Polyethelene Glycol Diacrylate10.0

This was a clear, transparent liquid with a viscosity of 110,000 cps.

The coating was poured onto a round, flexible decal of 2″ diameter. Thecoating was applied at a thickness of 0.08″. The decal was passed undera high intensity UV lamp at a conveyor speed of 20′/minute. The surfacetemperature of the coating was 155° C.

Adhesion was good. The cured coating had a 60° gloss of 85 and wastransparent. There was substantial curling of the decal.

Example 7

Two-Component Polyurethane/UV Curable Composition

A urethane acrylate was prepared with IPDI, hydroxypropyl acrylate and a4000 MW polyether diol in an equivalent ratio of 3/2/1. The reactionproduct was a clear, colorless liquid. At 25° C. the viscosity was12,000 cps.

Part A—Polyol

This urethane acrylate was added to the polyol of a typical polyurethanedoming resin formulation as seen below. In this example the urethaneacrylate was simply blended with the polyol. The hydroxy acrylatemonomer could also be reacted onto the isocyanate whereby the isocyanatewould contain two reactive groups, isocyanate and acrylate.

Polypropylene Glycol (423 MW triol) 53.00 Tinuvin P (UltravioletAbsorber - Ciba) 1.00 Dibutyltin Dilaureate (Catalyst) 1.00 Irganox 1010(Antioxidant - Ciba) 1.00 SF-96 (Surface Active Agent - GE Silicone)0.04 Urethane Acrylate 42.0 Irgacure 184 2.0 Irgacure 819 0.10 100.14

Part B—Isocyanate

Part B of this formulation can be prepared by reacting an aliphaticdiisocyanate with a polyol. The polyol can be a difunctional,trifunctional and/or tetrafunctional. This will form the isocyanateprepolymer. The dry polyol is mixed with the diisocyanate and heated to90° C. for one hour under 29″ of vacuum.

A typical formulation for the isocyanate is as follows:

Polypropylene Glycol (1000 MW diol) 40.00 Dicyclohexylmethane4,4′-diisocyanate 60.00 100.00

The dicyclohexylmethane 4,4′-diisocyanate is available from Bayer.

Equal volumes of Part A and Part B were mixed together in ameter-mix-dispensing equipment and applied onto the surface to be domed.The domed article was then passed under a high intensity UV lamp at aconveyor speed of 20′/minute. The surface temperature of the coating was48° C. A skin formed and the body of the dome, although not fully cured,became thick and did not flow immediately after exposure to the UVlight.

The coated decal was left to cure for 24 hours at 25° C. and 50%relative humidity. Adhesion was good. The cured coating had a hardnessof 80 D0 and a 60° gloss of 82. The dome was transparent. No curling ofthe decal was observed.

Example 8

Two-Component Epoxy/UV Curable Composition

An acrylate-epoxy oligomer can be made by acrylating an epoxy resin. Forexample, an epoxy resin can be acrylated in a two step reaction. In thefirst step, a hydroxy acrylate is reacted with an anhydride or a diacidto form an ester having a free carboxylic acid group and a free acrylategroup. The reaction occurs between a carboxylic group of the diacid oranhydride, and the hydroxyl group of the hydroxy acrylate. The resultingester is then reacted with an epoxy resin to form the acrylate-epoxyoligomer. The epoxy resin can be either aliphatic or aromatic. BisphenolA epoxy resin based acrylates are preferable to use with bisphenol Aepoxy doming resins.

There are many epoxy-acrylates commercially available that are suitablefor this application. Some examples are Laromer LR 9019 (BASF), Photomer3015 (Cognis) and CN-120 (Sartomer).

A suitable epoxy doming resin composition is prepared from the reactionof an epoxy resin with amine hardeners. To facilitate the application ofthe chemicals in production, the epoxy resin and amine hardeners areformulated into an easily handled two-component product. Part B, theamine hardener, is usually formulated to be used in a simple volumetricratio with the epoxy resin. A typical formulation for Part B is asfollows:

Part B—Epoxy Hardener

Polyoxypropyleneamine 30.00 Nonyl Phenol 18.00 CN-120, Epoxy AcrylateOligomer 50.00 Irgacure 184 Photoinitiator 2.0 100.00

The above formulation is simply mixed together. Heating is notnecessary. To form the epoxy doming resin, equal volumes of Part B andthe epoxy resin (Part A) are mixed together and applied onto thesubstrate to be domed.

Part A—Epoxy Resin

Epoxy Resin 100.00

A suitable epoxy resin is Epon 825 (Shell Chemicals). A suitable aminehardener is Jeffamine D-230 (Texaco Chemicals).

Equal volumes of Part A and Part B are mixed together inmeter-mix-dispensing equipment and applied onto the surface to be domed.The domed article was then passed under a high intensity UV lamp at aconveyor speed of 20′/minute. The surface temperature of the coatingreached 58° C. A skin formed and the body of the dome, although notfully cured, became thick and did not flow immediately after exposure tothe UV light.

The coated decal was left to cure for 24 hours at 25° C. and 50%relative humidity. Adhesion was good. The cured coating had a hardnessof 65 D0 and a 60° gloss of 82. The dome was transparent. No curling ofthe decal was observed.

Example 9

Cationic UV Curing System

UVR-6105 91.0 UVR-6000 9.0 UVI-6976 0.05 100.05

UVR-6105 is a cycloaliphatic epoxy resin. UVR-6000 is an aliphatic epoxydiluent. UVI-6976 is a mixture of triaryl sulfonium hexafluoroantimonatesalts. All these resins are available from Dow Chemical.

This was a clear, transparent liquid with a viscosity of 200 cps.

The coating was poured onto a round, flexible decal of 2″ diameter. Thecoating was applied at a thickness of 0.08″. The decal was passed undera high intensity UV lamp at a conveyor speed of 20′/minute. The surfacetemperature of the coating reached 109° C.

The dome continued to cure after exposure to the UV light. Followingexposure, samples were heated for 2 hours at 60° C., to complete thecure, including the “dark cure” process.

Adhesion was good. Hardness was 80D. The cured coating had a 60° glossof 84 and was clear and transparent. Some curling of the flexible decalwas observed.

Example 10

Cationic UV Curing System

UVR = 6105 45.5 Bisphenol A Epoxy Resin 45.5 UVI-6976 0.05

UVR-6105 is a cycloaliphatic epoxy resin. UVI-6976 is a mixture oftriaryl sulfonium hexafluoroantimonate salts. All the resins areavailable from Dow Chemical. The bisphenal A epoxy resin is availablefrom Dow Chemicals under DER 331.

This was a clear, transparent liquid with a viscosity of 2000 cps.

The coating was poured onto a round, flexible decal of 2″ diameter. Thecoating was applied at a thickness of 0.08″. The decal was passed undera high intensity

UV lamp at a conveyor speed of 20′/minute. The surface temperature ofthe coating reached 61° C.

The domes continued to cure after exposure to the UV light. Followingexposure, samples were heated for 2 hours at 60° C., to complete thecure, including the “dark cure” process.

Adhesion was good. Hardness was 80D. The cured coating had a 60° glossof 84 and was clear and transparent. No curling of the flexible decalwas observed.

Example 11

Cationic UV Curing System

UVR-6110 33.11 UVI-6976 0.67 Polyurethane Polyol 33.11 PolyurethaneIsocyanate 33.11 100.00

The polyurethane polyol and isocyanate formulations are given in Example7.

UVR-6110 is a cycloaliphatic epoxy resins. UVI-6976 is a mixture oftriaryl sulfonium hexafluoroantimonate salts. These resins are availablefrom Dow Chemical.

This is a clear, transparent liquid with a viscosity of 800 cps.

The coating was poured onto a round, flexible decal of 2″ diameter. Thecoating was applied at a thickness of 0.08″. The decal was passed undera high intensity UV lamp at a conveyor speed of 20′/minute. The surfacetemperature of the coating reached 55° C.

The domes continued to cure after exposure to the UV light. Followingexposure, samples were heated for 2 hours at 60° C., to complete thecure, including the “dark cure” process.

Adhesion was good. Hardness was 80D0. The cured coating had a 60° glossof 87 and was clear and transparent. No curling of the flexible decalwas observed.

Example 12

Silylated Polyurethane/Urethane Acrylate

Silylated Polyurethane Resin 80.00 Urethane Acrylate Oligomer fromExample 1 20.00 Irgacure 184 Photoinitiator 2.00

The coating was poured onto a round, flexible decal of 3″ diameter. Thecoating was applied at a thickness of 0.08″. The decal was passed undera high intensity UV lamp at a conveyor speed of 20′/minute. The surfacetemperature of the coating was 55° C.

A skin formed and the body of the dome, although not fully cured, becamethick and did not flow immediately after exposure to the UV light.

The coated decal was left to cure for 24 hours at 25° C. and 50%relative humidity. Adhesion was good. The cured coating had a hardnessof 45 D0 and a 60° gloss of 80. The dome was transparent. No curling ofthe decal was observed.

Example 13

Silylated Polyurethane/Acrylated Monomer

Silylated Polyurethane Resin 80.00 Tetrahydrofurfuryl Acrylate 20.00Irgacure 184 Photoinitiator 2.0

The coating was poured onto a round, flexible decal of 3″ diameter. Thecoating was applied at a thickness of 0.08″. The decal was passed undera high intensity UV lamp at a conveyor speed of 20′/minute. The surfacetemperature of the coating was 55° C. A skin formed and the body of thedome, although not fully cured, became thick and did not flowimmediately after exposure to the UV light.

The coated decal was left to cure for 24 hours at 25° C. and 50%relative humidity.

Adhesion was good. The cured coating had a hardness of 55 D0 and a 60°gloss of 82. The dome was transparent. No curling of the decal wasobserved.

Example 14

A silylated polyurethane doming resin, as described in co-pendingapplication Ser. No. 11/124,077, had a Shore D0 hardness of 40 whencured at 25° C. and 50% R.H. for 24 hours.

A urethane acrylate was prepared with IPDI and hydroxyethyl acrylate anequivalent ratio of 1/1. The reaction product was a clear, colorlessliquid. At 25° C. the viscosity was 400,000 cps. This radiation curedpolymer had a hardness of 90 D.

The two polymers were mixed according to the following formulation:

Silylated Polyurethane Resin 90.00 Urethane Acrylate Oligomer 10.00Irgacure 184 Photoinitiator 2.0

The coating was poured onto a round, flexible decal of 3″ diameter. Thecoating was applied at a thickness of 0.08″. The decal was passed undera high intensity UV lamp at a conveyor speed of 20′/minute. The surfacetemperature of the coating was 57° C.

A skin formed and the body of the dome, although not fully cured, becamethick and did not flow immediately after exposure to the UV light.

The coated decal was left to cure for 24 hours at 25° C. and 50%relative humidity. Adhesion was good. The cured coating had a hardnessof 70 D0 and a 60° gloss of 83. The dome was transparent. No curling ofthe decal was observed.

TABLE 1 Peak Viscosity Exotherm Hard- (cps Temp ness Shrinkage (%)Sample name at 25° C.) (° C.) (shore) Linear Density UV-curable 7919,000 85 63 DO 0.50 4.09 87 18,000 94 90 DO 0.64 55 54,000 104 90 DO1.12 4.40 29 13,600 104 82 DO 1.86 54 166,000 146 84 DO 2.14 UVcationic- 177 200 75 80 D 0 4.78 curable 2 component 808 1,000 26 70 DO0 5.06 polyurethane

While the invention has been described with respect to specific examplesincluding presently preferred modes of carrying out the invention, thoseskilled in the art will appreciate that there are numerous variationsand permutations of the above described systems and techniques that fallwithin the spirit and scope of the invention as set forth in theappended claims.

1. A method of preparing an article comprising a substrate and a curedcoating; comprising preparing a composition comprising anactinic-radiation curing polymer, applying the composition to thesubstrate to form coating having a thickness of at least about 0.5 mmand curing the composition with actinic radiation while maintaining atemperature of at most 150° C. to form the cured coating; wherein thecured coating has a hardness of about Shore A 90 to about Shore D
 90. 2.The method of claim 1 wherein the composition has a viscosity of 50 to20,000 cps.
 3. The method of claim 1 wherein the actinic-radiationcuring polymer is an acrylate polymer or a mixture of acrylate polymers.4. The method of claim 1 wherein the actinic-radiation curing polymer isa UV cationic curing polymer.
 5. The method of claim 1 wherein thecomposition further comprises a two-component epoxy or polyurethanepolymer.
 6. The method of claim 1 wherein the composition furthercomprises a moisture-curable silylated resin composition.
 7. The methodof claim 1 further comprising cooling the coating during curing.
 8. Amethod of preparing molded articles comprising preparing a compositioncomprising an actinic-radiation curing polymer, pouring the compositioninto a mold having a thickness of at least about 0.5 mm and curing thecomposition with actinic radiation while maintaining a temperature of atmost 150° C. to form the molded article; wherein the cured moldedarticle has a hardness of about Shore A 90 to about Shore D
 90. 9. Amethod of decreasing tack free cure-time of a two-part polyurethane orepoxy composition or a moisture curable silylated composition comprisingadding to the composition a sufficient amount of an actinic-radiationcuring polymer or acrylate monomer to reduce the tack-free time, andthen applying actinic radiation to the composition.
 10. The method ofclaim 9 comprising a two-part polyurethane or epoxy comprising adding tothe composition a sufficient amount of an actinic-radiation curingpolymer.
 11. The method of claim 10 comprising applying the actinicradiation while maintaining a temperature of at most 150° C.
 12. Themethod of claim 10 wherein applying the actinic radiation forms a skinon the outside of the coating.
 13. The method of claim 9 comprising amoisture curable silylated composition comprising adding to thecomposition a sufficient amount of an actinic-radiation curing acrylatepolymer or acrylate monomer.
 14. The method of claim 13 wherein applyingthe actinic radiation forms a skin on the outside of the coating.